The present invention relates to magnetic disk drives designed for use with exchangeable recording media, and more particularly to a diagnostic disk for checking the radial misalignment and the azimuthal misalignment of a magnetic head of such disk drives.
A magnetic disk drive controls writing and reading operation to and from an exchangeable recording medium such as a flexible disk (floppy disk). The disk drive has a motor-driven spindle for rotating the recording medium, a clamping mechanism for securing or releasing the recording medium to or from the spindle, a magnetic head for writing and reading information to and from medium, and a head-positioning assembly for moving the magnetic head in the radial direction of the recording medium to position the magnetic head at a distination track on the recording medium.
The disk drive is required to read such information from the recording medium that was recorded thereon by means of another disk drive. Accordingly, the head-positioning assembly in every disk drive should locate the magnetic head precisely at the absolute positions for all the tracks. Additionally, the transducer gap of the magnetic head should be perpendicular to the track center line. If the magnetic head radially deviates from the recording track or azimuthally deviates from the perpendicular line to the track center line, the amplitude of the output signal from the magnetic head may be so reduced that it cannot be recognized as the data. Thus, the disk drive without precise head alignment cannot read correctly the data which was recorded by the disk drive with precise head alignment, and vice versa.
The misalignment of the head is caused by a shock during shipment of the disk drive, and therefore, the head alignment is desired to be checked after settling of the disk drive.
For the purpose of checking the head alignment, a diagnostic disk is proposed in U.S. Pat. No. 4,513,331, entitled "METHOD AND APPARATUS FOR DISK DRIVE ALIGNMENT". The diagnostic disk includes progressively offset tracks for measuring the radial alignment of the magnetic head with respect to the track center line, and azimuth tracks for checking the azimathal angle of the transducer gap of the magnetic head with respect to the perpendicular line of the track center line.
The progressively offset track and the azimuth track are divided into a plurality of sectors, each having a sector identification field and a sector data field. In the progressively offset track, the sector data fields are progressively and alternatevely offset from the track center line in the inward or outward direction of the disk by an increasing value. That is, the proportion of a blank area in which no data is recorded gradually increases in the head read path of a perfectly aligned head in relation to the increment of the sector number. On the other hand, in the azimuth track, each of the sector data fields is recorded at an individual azimuth angle determined in correspondence to the sector number. The sector data are alternatively recorded at positive and negative angles with their absolute values gradually increasing in relation to the increment of the sector number. The data fields have a width equal to the track width.
In operation, the radial alignment of the magnetic head is measured by reading the progressively offset track, and then, detecting the identification field of the sector in which the sector data field can be recognized as the predetermined data. Similarly, the azimuth angle is measured by reading the azimuth track, and then, detecting the identification field of the sector to which the readable sector data belongs.
However, it is impossible with the prior art diagnostic disk to detect finely the values of the radial misalignment and the azimuth misaligned angle of the head, because the read/write circuit of the disk drive recognizes the output signal from the head only when the head offsets radially to a relatively great extent deflects azimuthally to a relatively large range, both with respect to the data track. For instance, the output signal from a head can be recognized only when the head is radially deflected from a track center line by 6 milli-inches or more or azimuthally deflected from a perpendicular line to a track center line by 40 minutes or more. In other words, the radial and azimuthal deflection cannot be detected at the precision less than .+-.6 milli-inch and .+-.40 minutes.